1. Field of the Invention
The present invention relates to a radiation light transducer for transducing a radiation ray like an X-ray Into light, a radiation image pickup device employing the transducer, a radiation image pickup system therefor, and a process for producing the radiation light transducer. In particular, the present invention relates to a radiation light transducer having a water-impermeable member capable of transmitting a radiation ray projected from the outside, a radiation image pickup device employing the transducer, a radiation image pickup system, and a process for producing the radiation light transducer.
2. Related Background Art
A roentogen examination apparatus employed in medical diagnosis should detect precisely an abnormal portion of a patient. Usual roentogen examination apparatuses convert the X-ray transmitted through a patient body or another examination subject into visible light or the like by means of a fluorescent screen, and a film in contact with the screen is exposed to the light. Although this conventional roentogen examination is sufficient in image resolution in a practical level, it has problems such that a long time is necessary from measurement to diagnosis, and the skill and extrasensory perception is required of the rentogenograph specialist for the location of the measurement region.
In recent years, a large-area sensor typified by amorphous silicon are developed to be reliable. By utilizing the merit of the amorphous silicon and the ease of enlarging the area thereof, the amorphous silicon are being developed for real-time roentogen examination with sufficient image contrast to raise the efficiency of abnormality diagnosis of the patient.
Generally, in detection of an X-ray image by a photoelectric transducer, an X-ray visible light transducer is necessary for transducing the radiation, namely the X-ray, to visible light. In the medical field, the transducer should have a large area suitable for roentogen examination of a thorax. A conventional transducer is constructed from a readily available fluorescent screen (a plate containing powdery phosphor) for film exposure with a large-area two-dimensional photoelectric transducer.
The radiation image pickup device which has a two-dimensional photoelectric transducer and a fluorescent screen bonded thereon is explained below.
FIG. 1A is a schematic plan view of a structure of a radiation image pickup device. FIG. 1B is a schematic sectional view of the device taken along line 1Bxe2x80x941B in FIG. 1A.
In FIG. 1A and FIG. 1B, photoelectric transducer 100 comprises base plate 101 made of glass or the like, element formation region 110 having a photoelectric transducer element or the like formed on base plate 101, and an electroconductive layer of aluminum or the like for wiring and connection electrode for electric connection with an external power source not shown in the drawing. Fluorescent screen 200, which is an X-ray visible-light transducer for wavelength conversion, comprises base board 201 made of PET (polyethylene terephthalate) or the like, and X-ray visible-light transducing layer 210 containing a phosphor particles for transducing the X-ray transmitted through base board 201 to visible light.
Photoelectric transducer 100 and X-ray visible-light transducer 200 are prepared respectively by separate processes. They are bonded together by an adhesive not shown in the drawing and fixed to complete the radiation image pickup device 1.
FIG. 2 is an enlarged sectional view of portion 2 indicated by a closed broken line in FIG. 15. This example of the photoelectric transducer having a two-dimensional light-receiving region has a base plate 101 made of glass or the like having a large area, and has therein a picture element input portion comprising photoelectric transducing element portion 120 employing amorphous silicon, and thin film transistor element portion 130, extending two-dimensionally. (Hereinafter, the thin film transistor is referred to as xe2x80x9cTFTxe2x80x9d.) The X-ray visible-light transducer employs a large-area fluorescent screen containing powdery phosphor.
In FIG. 2, photoelectric transducer 100 comprises, on base plate 101 made of glass or the like, photoelectric transducing element portion 120; TFT element portion 130, and element formation region 110 having wiring not shown in the drawing for driving the above elements, wiring for image signal readout, connection terminals for connection with external electric circuit, and so forth.
The respective layers constituting photoelectric transducing element portion 120 and TFT element portion 130 are constituted of lower electroconductive layer 102 composed of Cr, insulation layer 103 composed of hydrogenated noncrystalline silicon nitride layer, semiconductor layer 104 composed of an intrinsic hydrogenated noncrystalline silicon layer, n+ layer 105 composed of n+ type hydrogenated amorphous silicon, upper electroconductive layer 106 composed of aluminum, and semiconductor protection layer 107 composed of hydrogenated noncrystalline silicon nitride (xcex1-SiN:H) layer. These layers are formed by deposition by CVD, sputtering, vapor deposition or the like process, patterning, and are electrically tested for function confirmation.
The above materials for constituting the layers of photoelectric transducing element portion 120 and TFT element portion 130 are shown as examples only, and are not limited thereto.
X-ray visible-light transducer 200 is produced by forming X-ray visible-light transducing layer 210 by blending powdery phosphor particles 202 with binder 203, applying the blended matter on base board 201 made of PET or a like material, curing the binder to allow phosphor particles 202 to adhere and to fix on base board 201.
The obtained photoelectric transducer 100 and X-ray visible-light transducer 200 are bonded by adhesive 300 such as a silicone adhesive and an epoxy adhesive, and the adhesive is cured to prepare a radiation image pickup device.
This radiation image pickup device transduces the X-ray introduced from the side of base board 201 to visible light by X-ray visible-light transducing layer 210. This visible light is introduced to element formation region 110 on base plate 101 of photoelectric transducer 100 and is transduced to electric signals. This electric signals are read out by TFT element portion 130 on base plate 101 of photoelectric transducer 100 and external drive circuit (not shown in the drawing) to obtain electric signals for two-dimensional X-ray image.
However, base board 201 of X-ray visible-light transducer 200 is made of a moisture-permeable PET (polyethylene terephthalate), and binder 203 constituting the X-ray visible-light transducing layer 210 is a permeable resin. Base board 201 is fixed to element formation region 110 of photoelectric transducer 100 by adhesive 300 with interposition of X-ray visible-light transducing layer 210.
Therefore, when the radiation image pickup device is kept at a high humidity, base board 201 absorbs moisture, and the moisture is liable to penetrate through X-ray visible-light transducing layer 210 into element formation region 110. The moisture in element formation region 110 may cause deterioration and variation of characteristics of the photoelectric transducing element or other parts, or may cause disconnection of wiring by corrosion, thereby causing problems in long-term environmental stability of the photoelectric transducer.
Further, X-ray visible-light transducer 200 employs a fluorescent screen prepared by cutting a large fluorescent plate into pieces of a desired size. Even if the external face of base board 201 is covered with a metal such as aluminum by bonding with an adhesive, moisture can penetrate into base board 201 from its edge side. Therefore, the penetration of moisture into element formation region 110 cannot readily be prevented completely.
In X-ray visible-light transducing layer 210, phosphor particles are not packed at a sufficiently high packing density owing to the presence of binder resin 203, thereby efficiency of transducing the X-ray to visible light being lower. The increase of the packing density of phosphor particles 202 makes the entire of X-ray visible-light transducing layer 210 brittle, resulting in difficulty in handling.
Increase of the thickness of X-ray visible-light transducing layer 210 for improving the X-ray visible light transduction efficiency will cause scatter or absorption of the transduced light by binder 203, phosphor particles, and their interface. Thereby, the efficiency of the visible light generated by the transduction to reach photoelectric transducing element region 120 may be lowered, and the increase of the scattered light will lower resolution of the image. In particular, in use of the two-dimensional radiation image pickup device for human diagnosis, the quantity of the X-ray from radiation source should be decreased to minimize the X-ray exposure dose to a human body. The drop of the resolution and sensitivity by scattering is the problem to be solved. Therefore, the thickness of X-ray visible-light transducing layer 210 is usually set at about 150 xcexcm.
Another X-ray visible-light transducer is disclosed In which the phosphor is packed at a packing ratio of 100% by using a fluorescent material like CsI, and forming crystalline matter by vapor deposition or a like process without using binder 203. However, this type of transducer deteriorates significantly in the characteristics (X-ray visible-light transducing efficiency), and moisture will readily penetrate through the surface of base board 201, making difficult the maintenance of the characteristics throughout the period of use.
An object of the present invention is to provide an X-ray visible-light transducer which does not allow moisture to penetrate into an element formation region of a photoelectric transducer through a substrate such as an X-ray visible-light transducing substratum, without increasing the steps of the transducer production.
Another object of the present invention is to provide a radiation light transducer (e.g., X-ray visible-light transducer) which can maintain light transmission efficiency and resolution without scattering or absorption of light by a binder, powder particles, or the interface thereof even with an increased thickness of the transducing region.
A further object of the present invention is to provide a radiation image pickup device employing the above radiation light transducer, a radiation image pickup system, and a process for producing the radiation light transducer.
According to an aspect of the present invention, there is provided a radiation light transducer comprising a substrate comprised of a water-impermeable member which transmits radiation projected from outside, and a wavelength transducing means which transduces the radiation transmitted through the substrate to light, wherein the substrate has a cavity to cover the edge face of the wavelength transducing means.
According to another aspect of the present invention, there is provided a radiation light transducer comprising a substrate comprised of a water-impermeable member which transmits radiation and having a cavity on one face thereof, a wavelength transducing means provided in the cavity of the substrate for transducing the wavelength of the radiation, the wavelength transducing means being in contact, at one face and adjacent edge face thereof, with the inside face of the cavity of the substrate.
According to a further aspect of the present invention, there is provided a radiation image pickup device comprising the above radiation light transducer, and a photoelectric transducer for transducing the above transduced light further to electric signals.
According to a further aspect of the present invention, there is provided a radiation image pickup system comprising the aforementioned radiation image pickup device, an irradiating means for projecting radiation to the radiation image pickup device, which irradiating means consists of a radiation source, a signal processing circuit for processing the signals from the photoelectric transducer, a storing means for storing signals from the signal processing circuit, a displaying means for displaying the signals from the signal processing circuit, and a transmission-treatment means for transmitting the signals from the signal processing circuit.
According to a further aspect of the present invention, there is provided a process for producing the radiation light transducer comprising the steps of forming a hollow on a substrate comprised of a water-nonpermeable member capable of transmitting radiation projected from the outside, and forming a wavelength transducing means for transducing the radiation transmitted through the substrate to light.
According to a further aspect of the present invention, there is a process for producing the radiation light transducer comprising the steps of forming a cavity on a substrate capable of transmitting radiation, and forming on the cavity a wavelength transducing means for transducing the wavelength of the radiation.
According to the present invention, the lateral edge face of the wavelength transducing means for transducing the radiation to light is covered with the substrate, whereby penetration of moisture into the photoelectric transducer can be prevented and the wavelength can be transduced stably for a long term.